Neptune-sized GJ 436b is about 33 light-years from Earth in the constellation Leo, and GJ 1214b, a super-Earth, is about 42 light-years from Earth in constellation Ophiuchus. Earth- to Neptune-sized exoplanets make up most of the distant worlds discovered to date. But it's hard to know what the atmospheres and other features of these planets look like because the solar system doesn't have planets that fall between Earth's size and Neptune's.